The invention at hand is related to the head box of a fibrous web machine. More precisely the subject of the invention at hand is a method and an arrangement for managing a lamella vibration of a lip channel of a head box and the lamella for the lip channel of the head box.
In this context, the term head box stands for a unit of a fibrous web machine, as for example a paper machine, a board machine, a pulp drying machine, a tissue machine or similar, which is used in creating mass suspension before the forming unit. The function of the head box's function is to extend the mass suspension throughout the whole width of the fibrous web machine in a homogeneous flow that proceeds as a regular front. The mass suspension is fed from the head box's lip channel in the forming part. The head box's most common problems and weak points that are caused inhomogeneously and/or irregularly                in the flow direction, and/or        proceeding in a transversal lateral/vertical direction as for the flow direction from the mass flow of the mass suspension, various turbulences in the lip channel of the head box, lamellas' vibration problems, streak formation and other structure problems of the fibrous web line, such as level anomalies and blisters in the fibrous web.        
In this context, the term lip channel stands for a channel throughout which the mass suspension flows through the head box in the machine direction or MD-direction through the nozzle part to the forming section. If the head box multi-layer and/or single-layer structured and has been realized with the so called long lamellas that extend in the MD-direction through the slice, the nozzle part has not necessarily been arranged in the structure, but the mass suspension flows through the slice into the forming section.
In this context, the term laminated structure, which is commonly also called “separation lamella”, spline or whalebone, stands for at least one lamella situated in the head box's lip channel and extends                in the machine direction or MD-direction near the slice at the end of the lip channel or even out from the slice, and        in a transversal or CD-direction as for the MD-direction to the lip channel's width, and which is used in the lip channel to separate, in a vertical or Z-direction as for the MD-direction, from each other two or more single suspension flows which have the same or different viscosities, mass consistencies and/or chemical characteristics.        
In this context, the definition lamella's border area stands for the end area or the head area of the lamella,                which extends in the CD-direction to the whole width of the lip channel,        which extends in the MD-direction near the slice or through the slice, and        over which mass suspension flows.        
The definition lamella's head stands for, in this context, in the MD-direction the lamella's remotest edge that extends in the CD-direction throughout the whole width of the lip channel through which the mass suspension flows into the slice or over/through it.
It is already common knowledge that laminated structures are used in the fibrous web machine's head box's lip channel. The lamellas can be regarded to be already sufficiently well known to an average craftsman. It is although necessary to notice that the lamellas' main purpose is, due to an increased turbulence production, to lower the tensile ratio of the fibrous web, as for example paper or board. In addition, with the help of the lamellas one can try a) to decrease the scale of the emerged turbulence, in which case effective factors are for example minor channel height, increased boundary layer turbulence and thin trailing head, and b) to prevent the confusion of the flows coming from different lines of the turbulence generator.
It is also already common knowledge that the problem is that the vibration of the lamella used in the head box's lip channel causes striation in the fibrous web, as for example in the paper web. Regarding yet this problem it can be noticed that the cockling of the lamella's trailing head can cause interferences in the flow that can be seen in the finished web as streaks.
In the patent specification FI 113382 is known a procedure to avoid or to reduce the turbulences that occur occasionally in the head box's lamellas, in a flow that goes through the paper machine's head box, when after the closed rear edge it develops a blind area. The publication suggests that the blind area should be rinsed with several minor flows, conducted from the main flow, that are formed with channels created in the lamella's surface. In order to realize the procedure the F10-publication suggests as the head box's lamella solution as follows.                The lamella's final part has, as for the MD-direction, grooves that have been made forming at the edge of the lamella as if saw teeth or shoulders that are at least partially rounded.        There are grooves in the lamella that are in the lamella's border area and in the same direction as the flow, in which case the grooves seen from above are rectangular or parabolic or shaped as a spline, in which case the broad side of the spline indicates in the flow's direction.        
The basic idea of the patent specification FI 113382 is, therefore, that in the MD-direction the lamellas' border area or border has been shaped in order to reduce the emergence of flow interferences like vortices and turbulences, and thus to reduce the vibration created in the lamella. The solution for the lamella suggested by this FI publication requires a remarkable knowledge of flow technique and requires, in order to realize a functional flow solution, from the forming of the border area a particularly remarkable precision. In addition, the weak point of this solution is that it can work only as a basis for the planning in a chosen, restricted mass flow area.